TESTING THE GOODNESS-OF-FIT OF INFILTRATION MODELS FOR HIGHLY PERMEABLE SOILS UNDER DIFFERENT TROPICAL SOIL-MANAGEMENT SYSTEMS

The Kostiakov, modified Kostiakov (A), modified Kostiakov (B), Philip, modified Philip (A) and modified Philip (B) infiltration models were tested for their ability to describe water infiltration into highly pe rmeable sandy soils from the Nsukka plains of SE Nigeria. Infiltration data were obtained on field plots with the following management syste ms: tilled-mulched, tilled-unmulched, untilled-mulched, untilled-unmul ched and continuous pasture. On all treatments, the cumulative infiltr ation values predicted by the classical Kostiakov, Philip and modified Philip (A) models deviated most from the experimental data. The other models produced values that agreed very well with the measured data. Considering the ease of determining the fitting parameters it is propo sed that on soils with high infiltration rates, either the modified Ko stiakov model (I = Kt(a) + I(c)t) or modified Philip model (I = St(1/2 ) + I(c)t), (where I is cumulative infiltration, R is the time coeffic ient, r is the time elapsed, a is the time exponent, I-c is the steady infiltration rate and S is the soil water sorptivity), be used for ro utine characterisation of the infiltration process.